This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C.xc2xa7xc2xa7119 from an application for MICROWAVE OVEN HAVING A PREVENTING OVERHEAT AND METHOD FOR OPERATING A FAN MOTOR OF THE MICROWAVE Oven earlier filed in the Korean Industrial Property Office on Nov. 8, 2000 and there duly assigned Ser. No. 66146/2000 by the Office.
1. Field of the Invention
The present invention relates to a microwave oven having an overheat preventing function and a method of controlling its fan motor. More specifically, the present invention relates to a microwave oven which controls the turning speed of its fan motor variably in response to an output level of its magnetron, and increases the turning speed of a cooling fan when the magnetrons output is high, thereby preventing its electrical components from being overheated, and further relates to a method of controlling its fan motor.
2. Description of the Related Art
A microwave oven is a cooking appliance that cooks food rapidly by using microwaves, and has a high-voltage transformer and a magnetron. The high-voltage transformer produces given high voltages to drive the magnetron, and this magnetron emits microwaves of high frequencies (about 2,450 MHz) to the inside of its cooking chamber in which food is held. The microwave moves the molecules of the food being cooked at high speeds, and the food is cooked by friction heat generated by the movement of the molecules.
Referring to FIG. 1, this conventional microwave oven includes a main body 20 forming the outer appearance of the oven, a cooking chamber 22 provided to one side of the main body 20 and opened in the front, and an electrical component compartment 23 provided to the other side and housing a lamp 2, a cooling fan 3, a magnetron MGT, a high-voltage transformer HVT, a high-voltage condenser HVC, etc. A control panel 25 having a display and operating buttons is located on the front of the compartment 23. A door 21 is hinged on one side of the front of the main body 20 to open and close the cooking chamber 22. A tray 24 is mounted on the floor of the cooking chamber 22, and food to be cooked is put on this tray 24. The tray 24 is turned by a driving motor and gears (not shown) provided to the bottom of the main body 20 to enhance the cooking efficiency.
Simultaneously with actuating the magnetron MGT to cook the food on the tray 24, the fan motor (not shown) is driven to turn the cooling fan 3. The outside air is introduced to the inside of the compartment 23 by the action of the cooling fan 3 to cool the electrical components on a printed circuit board of the respective magnetron MGT, high-voltage condenser HVC, high-voltage transformer HVT, and control panel 25. The fan motor keeps the constant turning speed without regard to an output level of the magnetron.
There are several methods of controlling the output level of the magnetron for the conventional microwave oven, which is fully described as follows.
The first one is a method of controlling the magnetron MGT""s output in response to a voltage applied to the transformer HVT""s secondary winding by varying the number of the transformer HVT primary windings turns. In other words, an intermediate tap is provided to the primary winding of the transformer HVT, and power is then applied by turning on a relay connected to this intermediate tap. As a result, the number of the primary winding""s turns is decreased, and a voltage higher than normal one is applied to the transformer HVT so that the magnetron MGT""s output is high.
The second one is a method of controlling the magnetron MGT""s output by varying the number of the transformer HVT secondary winding""s turns, instead of keeping the number of the transformer HVT primary winding""s turns. In this occasion, as the number of the transformer HVT""s secondary winding is increased, the transformer HVT""s volume is inevitably increased.
The third one is a method of controlling the magnetron MGT""s output by adjusting the ratio of the turned-on time for applying the power and the turned-off time for cutting off the power supply. More specifically, if the turned-on time is reduced and the turned-off time is increased by controlling a power relay, the magnetron""s output is low. On the contrary, if the turned-on time is increased and the turned-off time is decreased, the magnetron""s output is high.
In case of using the conventional microwave oven in high-output mode by increasing the magnetron""s output, the surface temperature of the respective electrical components along with the magnetron in the electrical component compartment is inevitably raised more than in low-output mode. If a user does not take any proper step, the electrical components are overheated and malfunction, thus being reduced in life.
When the magnetron""s output is high, the cooling fans turning speed needs to be increased to drop the inside temperature of the electrical component compartment rapidly. However, since the cooling fan used for the conventional microwave oven operates at constant turning speed, it cannot cool the electrical components rapidly in high-output mode. More specifically, the turning speed of the cooling fan depends on the driving speed of the fan motor, and the conventional fan motor is preset to be driven at constant turning speed suitable for normal output mode. Accordingly, the fan motor is driven by the preset number of revolutions without regard to the output level of the magnetron, so it cannot operate satisfactorily in high-output mode.
Considering the above matter, a fan motor that can be driven by the large number of revolutions to meet the high-output mode may be used. However, this motor is not proper one for the low-output mode. Continuously driving the fan motor even in the low-output mode causes the unnecessary power consumption.
Thus, there is a need to develop a technique of driving the fan motor at low speeds if the magnetron""s output is low to decrease the power consumption, and driving the fan motor at high speeds if the magnetron""s output is high to prevent its electric components from being overheated.
It is an object of the present invention to provide a microwave oven which controls the turning speed of its fan motor variably in response to an output level of its magnetron and increases the turning speed of a cooling fan when the magnetron""s output is high, thereby preventing its electrical components from being overheated, and a method of controlling its fan motor.
In order to achieve the above object, the present invention provides a microwave oven capable of cooking food according to an output mode in response to an output level of its magnetron, including a fan motor having a low-speed node and a high-speed node to receive power, and having a turning speed variable in response to a node connecting state; an output mode selecting part through which one of output modes is selected; a switching part having at least one switch for switching power applied to the low-speed node or high-speed node of the fan motor; and a control unit controlling the switching part in response to an output mode selected by the output mode selecting part.
According to another aspect of the present invention, a microwave oven capable of cooking food according to an output mode in response to an output level of its magnetron, includes a fan motor having a plurality of nodes as a power input terminal, and having a turning speed variable upon receipt of a power through the nodes; an output mode selecting part through which one of plural output modes is selected; a switching part for switching the power applied to the fan motor""s input terminal; and a control unit controlling the switching part in order to set up the fan motor""s turning speed in response to an output level of the magnetron corresponding to an output mode selected by the output mode selecting part .
According to still another aspect of the present invention, a method of controlling a fan motor for a microwave oven capable of cooking food according to an output mode in response to an output level of its magnetron, includes the steps of (a) determining if an output mode is selected; (b) if a low-output mode is selected in the step (a), performing a cooking according to the low-output mode by applying a power to the fan motor""s low-speed node; and (c) if a high-output mode is selected in the step (a), performing a cooking according to a high-output mode by applying the power to the fan motor""s high-speed node.
The step of performing the cooking according to the high-output mode includes the substeps of (d) driving the magnetron in a high-output level; (e) driving the fan motor at high speeds by applying the power to the fan motor""s high-speed node; (f) checking if the high-output mode is completed; and (g) if the high-output mode is completed in the step (f), stopping the magnetron""s operation.
According to still another aspect of the present invention, a method of controlling a fan motor for a microwave oven capable of cooking food according to an output mode in response to an output level of its magnetron, includes the steps of selecting a user-desired output mode through a key input part; driving the magnetron according to an output level corresponding to the selected output mode; and switching a power applied to the fan motor""s input terminal so as to increase the fan motor""s turning speed as the magnetron""s output level is increased.
According to still another aspect of the present invention, a method of controlling a fan motor for a microwave oven capable of cooking food according to an output mode in response to an output level of its magnetron, includes the steps of (1) selecting desired one of plural output modes; (2) if a low-output mode is selected in the step (1), performing a cooking according to the low-output mode by applying a power to a low-speed node of the fan motor""s plural input terminals; (3) if a high-output mode is selected in the step (1), performing a cooking according to the high-output mode by applying the power to a high-speed node of the fan motor""s plural input terminals; and (4) after cooking food according to the low-output mode or high-output mode has been completed, performing a deodorization mode to remove the smell produced by cooking the food to the outside.